Conventional peanut butter and other nut butters typically comprise cohesive, comminuted mixtures of solid nut particles suspended in oil (nut paste), a sweetener such as sugar, high fructose corn syrup or honey, salt and a stabilizing agent (e.g., a high melting point fat or hardstock) to prevent separation of the oil and particulates. The primary component of peanut butter, peanut paste, is formed by roasting, blanching, and grinding shelled peanuts. During the grinding step, the cellular structure of the peanuts is ruptured, releasing the peanut oil in which the pulverized peanut solids become suspended.
There are a number of factors that consumers consider in evaluating the desirability of peanut butter. One is its "stickiness" perception. The consumer perceives "stickiness" as the adhesion to the roof of the mouth of the mass of ingested peanut butter, as well as the effort it takes for the tongue to remove it therefrom. However, what the consumer senses as "stickiness" is not due primarily to adhesive forces, but instead to the cohesiveness of the mass of peanut butter as it is worked on jointly by chemical (saliva) and physical (tongue) forces in the mouth. Indeed, "stickiness" decreases as the saliva and tongue reduces the viscosity of this mass of peanut butter to the point that it can be easily swallowed.
Another factor considered by consumers is "peanut flavor" perception. The mechanism by which peanut flavor is released is believed to be due to the hydration of the nut solids in the mouth by saliva. While the total amount of peanut flavor present in the nut solids is important, it appears that the ability to effectively hydrate these nut solids primarily affects peanut flavor intensity. Indeed, the more uniform the hydration of these nut solids, the more intense will be the perceived peanut flavor.
Prior efforts to reduce the stickiness perception of peanut butter without adversely affecting peanut flavor intensity have generally been unsuccessful. In the past, there has usually been a trade off between stickiness reduction and peanut flavor intensity, i.e., increases in peanut flavor also increase stickiness and vise versa. For example, chunky type peanut butters made with larger peanut granules have more peanut flavor compared to creamy style peanut butters. However, the processing conditions that create these larger particle size peanut solids generally lead to stickier peanut butters because of increases in viscosity. Conversely, fine grinding of the nut solids (i.e., reducing the particle size) disperses flavor components throughout the nut paste, thus decreasing the flavor impact of these nut solids.
The viscosity of the peanut butter is affected primarily by the particle size distribution (PSD) of the nut solids. Peanut butters made by milling the nut solids to a monomodal particle size distribution have relatively lower viscosities. See U.S. Pat. No. 5,079,207 (Wong et al), issued Jan. 7, 1992 (roll milling nut solids to a monodispersed/monomodal particle size distribution). Conversely, a courser grind results in a more viscous peanut butter because the nut solids exist in a polymodal particle size distribution, resulting in an increase in particle packing behavior and a greater tendency under stress of the nut particles to collide with each other. Another reason for the higher viscosity of polymodal PSD peanut butters is that coarse grinding of the nuts ruptures fewer oil cells, resulting in less free oil in the nut solid suspension.
To reduce stickiness, the viscosity of the peanut butter needs to be reduced. This can be achieved by increasing the amount of shear imparted to the nut paste and/or decreasing the particle size of the nut solids. A high pressure or multiple pass homogenization of the peanut paste has typically been used to achieve the necessary size reduction and shear. See, for example, U.S. Pat. No. 3,619,207 (Dzurik et al), issued Nov. 9, 1971 which describes one such high pressure homogenization process. Unfortunately, prior attempts to reduce the viscosity of the peanut butter have also led to a significant reduction in peanut flavor intensity. This has been attributed to a reduction in the residence time in the mouth of the mass of ingested peanut butter. This shorter in-mouth residence time decreases the peanut flavor intensity because the solids are hydrated to a lesser extent. In addition, high pressure or multiple pass homogenization often grinds the nut solids to such a fine size that a significant portion of the peanut flavor volatiles originally present are lost.
Another factor affecting consumer acceptability of peanut butter is its grittiness impression. Grittiness occurs when the solid particles in the peanut butter are of a sufficient size and appropriate geometry that the tongue can sense them. Solids that can impart grittiness include not only the peanut solids, but also other non-fat solids that are typically present in the peanut butter, especially water soluble solids such as sugar and salt. One way to reduce this grittiness impression is by simply passing the mixture of peanut paste and other non-fat solids through a high pressure homogenizer to reduce all the solids to a finer size. See U.S. Pat. No. 5,518,755 (Wong et al), issued May 21, 1996. However, as noted before, this also adversely impacts the peanut flavor intensity of the resulting peanut butter because of the size reduction that occurs in the peanut solids.
Accordingly, it would be desirable to be able to formulate a peanut butter that: (1) reduces the stickiness impression; (2) does not adversely affect peanut flavor intensity; and (3) reduces grittiness.